This invention relates to a method and composition for providing cathodic protection to metal structures and, more particularly, relates to a method and composition for providing cathodic protection to steel structures buried or partially buried in the ground.
Many underground steel structures such as pipelines, tanks and the like which are buried or partially buried in the ground, particularly large tanks and large-diameter pipelines and pipe risers, cannot be properly cathodically protected from corrosion. The buried surfaces of underground steel tanks, for example, are usually buried in sand and the like granular backfills and their aerated topside surfaces often require about 25 times the protective current density as their anaerobic bottoms. As a result of oxygen diffusion where protective coatings have failed or do not exist, it has often proven difficult or not feasible to prevent corrosion of bare and poorly coated tanks by applying cathodic protection with either galvanic and/or impressed current uniformly over entire steel surfaces.
It is a principal object of the present invention to cathodically protect the entire external surface of an uncoated or coated underground steel storage tank or the like buried steel structure.